Human Health and Diseases

Immune System

The immune system of the body is the essential aspect of our survival. If an immune system is absent then the body is very easily susceptible to infections caused by bacteria, virus, and various other pathogens. Let us learn about this unique system.

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Uniqueness of the Immune System

The human immune system is very unique. It is spread throughout the body, involving several types of cells, tissues, organs etc. A significant characteristic feature of this immune system is that it can distinguish between the body tissue and a foreign tissue. Even dead and faulty cells can be recognized by the immune system, which is cleared away from time to time by the immune system.

The immune system also has a role to play in allergic reactions, organ transplantation, and autoimmune diseases. It can be said that the immune system is majorly responsible for keeping us in good health.

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Immune System


Human Immune System

Immune System

Organs of the Immune System (Source – Wikimedia Commons)

The human immune system consists of tissues, cells, soluble molecules like antibodies and lymphoid organs. The white blood cells called the leucocytes have a significant role as they seek out to destroy the disease-causing organisms. These leucocytes are stored in different locations in the body including the spleen, bone marrow, and thymus. And therefore these organs are called as the lymphoid organs. The leucocytes are also present in the lymph nodes of the body.

The bone marrow is considered as the main lymphoid organ. It produces all the blood cells including the lymphocytes. The thymus is an organ that is present near to the heart, beneath the breastbone. It is very large at the time birth and gradually reduces in size.

In the bone marrow and the thymus, the immature lymphocytes differentiate and become antigen sensitive lymphocytes. Once they are mature, they migrate to the other secondary lymph organs such as the spleen, lymph nodes, tonsils, appendix, and Peyer’s patches of the small intestine. The secondary lymphoid organs are the sites where the lymphocytes interact with the antigen and then proliferate to become effector cells.

The spleen is a large organ that contains lymphocytes and phagocytes. It filters the blood and traps the microorganisms that are blood borne. Lymph nodes are small structures that are present in the lymphatic system of the body. They also trap the microorganisms that are present in the lymph or tissue fluid. The antigens in the lymph activate the lymphocytes and cause the immune response.

Immune System

Solved Questions For You

Q: Which lymphoid organ is large in size at birth, but gradually reduces in size?

  1. Spleen
  2. Thymus
  3. Pituitary
  4. Thyroid

Ans. The thymus is a lymphoid organ that is large in size at the time of birth. By the time a person reaches the age of puberty, it shrinks in size and becomes a small organ.

Q: To which type of barriers under innate immunity, do the saliva in the mouth and the tears from the eyes belong?

  1. Physiological Barriers
  2. Physical Barriers
  3. Cellular Barriers
  4. All of the above

Ans: The correct option is “A”. The immune system provides both the types of immune response innate and acquired immune responses. Innate immunity occurs naturally due to genetic factors or physiology.

It is a native immune response that present by birth. It provides physical barrier such as skin, Physiological barriers such as pH of the stomach, bile juice, saliva and tears, cellular barriers such as leucocytes, macrophage cell, and cytokine barrier.

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